Press brake die retainer



OC- 4, 1965 H. s. ACHLER ETAL 3,276,239

PRESS BRAKE DIE RETAINER Filed April 6, 1964 45- mw 17mm United States Patent Oiice 3,276,239 Patented Oct. 4, 1966 3,276,239 PRESS BRAKE DIE RETAINER Howard S. Achler, Harold Kaufmann, and Herman H. Lerner, Chicago, Ill., assignors to Kaufmann Tool and Engineering Corp., Chicago, Ill., a corporation of Illinois Filed Apr. 6, 1964, Ser. No. 357,664 S Claims. (Cl. 72-465) This invention relates to female press brake dies and more particularly relates to a simplified extruded pad reta-incr for urethane rubber die pads.

Urethane rubber, manufactured and sold by Du Pont under the trademark Adiprene has certain desirable characteristics, such `as unusually high load bearing capacity, abrasion resistance, and oil resistance. The potential use of urethane rubber for tooling, such as a substitute for the female die in press brakes has been known, and its superiority in versatility, economy and performance, by reducing tooling time, eliminating the need for a machined met-al female die, in producing sheet metal parts without scratched or gouged exterior surfaces, practin cability for long production runs, `and in producing sharper and more precise bends, has been demonstrated.

When loads, such -as from hard press brake punch, are applied to a die pad of urethane rubber, the extreme resiliency characteristic of the urethane rubber permits the pad to temporarily deform to -a precise female die shape conforming to the shape of the brake punch, while at the same time the material of the pad is .temporarily displaced laterally in all directions and oppositely from the press brake punch. The die pad, being confined in a die retainer, develops high bottom and lateral or side pressures. Furthermore, since urethane rubber is noncompressible, as constrasted to being deformable, it has the effect of being a solid liquid and performs like a confined hydraulic fluid within the limitations of its defiection rating.

Die retainers have, of course, been used and known where the entire retainer is built up of individual parts defining respectively `the bottom, two sides, and two end walls, with the end walls connected to the terminal ends of the bottom and sides. There are a number of drawbacks resulting from such prior constructions, namely: the relatively high labor cost in effecting the assembly of the multiple parts; the fact that the length of the bottom and sides require precise tailoring in size to the length of the die pad to be used, thus requiring large expense of a tailor-made retainer for each die pad of different length; the cost of machining of a bottom or building up a bottom to define a relief space for receiving distortion of the die pad thereinto during a brake punch operation; and the engineering of varying lthicknesses, of side walls and appropriate bracing therefor to accommodate variations in the maximum bending stresses developed at the lower edges of the side Walls Vand so as to avoid, to `as great an extent as possible, any variation during use in the ybasic shape of the retainer chamber for the die pad, so as to obtain the benefits of the aforenoted characteristics of the urethane rubber.

It is submitted that the versatility and economy of use of urethane rubber die pads would be additionally increased by the provision of a simplified and inexpensive die retainer for such d-ie pads and, accordingly, it is one object of this invention to provide an improved and simplified form of die retainer for urethane rubber die pads.

Another object of this invention is to provide a die retainer for urethane rubber die pads that provides t-he necessary strength for lateral and bottom pressures and for bending stresses developed when the die pad is used with a press brake punch, and which die retainer is characterized by its economy and simplicity of construction, Iand by its versatility in use and in the modification thereof for va-rying installations.

With these and other objects in view, our invention consists in the construction, arrangement `and combination of the various parts of our press brake die retainer, whereby `the objects above contemplated are attained, as hereinafter more fully set forth, pointed out in our claims and illustrated in detail on the accompanying drawing, wherein:

FIGURE l is a fragmentary isometric view of our invention showing a urethane -rubber die pad and its improved retainer therefor;

FIGURE 2 is a cross-section view taken substantially on line 2-2 of FIGURE l;

FIGURE 3 is a cross-section view of the end plate of the die pad retainer and is taken substantially online 3-3 of FIGURE l, and

FIGURE 4 is a cross-section view similar to FIGURE 2 but illustrating a typical use of the device of FIGURES 1 3 with a press brake punch in the forming of a sheet metal part.

Referring now to t-he drawing, FIGURE l shows a fiat urethane rubber die pad 10 and the improved die pad retainer generally indicated as 20. More specifically the die pad is an elongated block of urethane rubber whose cross-section is right rectangular thereby defining top surface 12 and parallel bottom surface 141, and parallel side surfaces 16 and 18.

The die pad retainer 20 includes an elongated channelshaped metal extrusion 21, preferably of aluminum, which denes an elongated die pad recess that is bounded by pad-engaging side walls 22 and 24, a pad support wall 26 formed by spaced surfaces 26a and 26h, corner relief recesses 28a and 28h, ya large central relief spiace or Well 30 and rounded corners 32a and 32b at the junction between the well 30 and the pad `support 26. The retainer 20 is formed with a fiat top 33, fiat bottom 34, and with a downwardly projecting elongated tail or tang 36 for purposes of alignment or clamping thereof, that extends longitudinally of the retainer and is located in a medial vertical plane of the extrusion. To provide for perfect squareness between bottom 34 and tang 36 in an extrusion, corner reliefs 37 are provided.

The shape of the extrusion is such that the thickness of the material behind, or outwardly, of side walls 22 and 24 gradually and continuously increases in lthickness from the least amount Vof material at the top of the side walls to a greater thickness at the level of the support wall 26. This gradually and continuously increasing material thickness is achieved by providing 'arcuate exterior walls 38 and 40. While the increase in thickness to accommodate increase in bending stresses could be achieved by downwardly and outwardly inclined outer surfaces, exterior `walls 38 and 40 are provided in arcuate shape for aesthetic reasons. When the walls 38 and 40 are circular arcs, the center of curvature must be located in the central vertical plane of extrusion 21 at the plane of support wall 26 or therebelow.

In the forming of the extrusion 21, the surfaces 26 and bottom 34 are provided precisely parallel, and side walls 22 and 24 are provided precisely parallel and at a spacing slightly larger than the width of the die pad to be used. The plane of surface 26 is precisely square with walls 22 and 24. The width of relief well 30 is about one-half of the width of the pad 10, and the depth of well 30 is between 25% to 30% of the thickness of pad 10. The spacing between the planes of top 33 and support wall 26 is less than the thickness of pad 10, so that pad 10 normally protrudes slightly above the upper surface 33 of the pad retainer, as best seen in FIGURES 1-3.

The pad retainer is also provided with a pair of similar end walls 42, only one of which is seen in FIG- URE 1. The end wall 42, 'as can be seen from FIGURES 1 and 3, is shaped generally to fit closely within the contour of the rectangular recess defined by the intersecting planes of walls 22 and 24 and surfaces 33 and 26, and additionally includes a tab 42a which fits into well 30. It is preferred that each end wall be spaced axially from the terminal end of the extrusion 21, as seen in FIG- URE l. In order to secure the end wall 42 at its desired location and to provide the necessary strength for resistance to forces thereagainst from the urethane rubber pad 10, elongated apertures 44 are provided extending into and through the material of the extrusion in a plane perpendicular to the longitudinal axis of extrusion 21. In the specific construction disclosed herein, two elongated bolts 46, with countersunk heads 46a having internal wrench sockets, and with threaded tip 46b are screwed into extrusion 21 and extend through walls 22 and 24 and through end wall 42. In effect, each of the end walls 42 carry lateral extensions in the form of the protruding shank portions of bolts 46 which cooperate with the longitudinal sect-ions of the extrusion 21, so that forces from pad 10 applied to fthe end walls 42 are transmitted lthrough bolts 46 to the transversely apertured sections of extrusion 21.

FIGURE 4 illustrates a typical use of the device of FIGURES 1-3, wherein a pr-ess brake punch P is in the process of forming a corner in -a sheet metal par-t W, and the urethane rubber die pad 10 has deformed fto form the female die for the work W. It is understood that the flat bottom 34 may be resting on the bed of the press brake machine yand `that tank 36 extends through a slot in the press brake bed normally provided for purposes, among others, of alignment. It will be seen how, under pressure from punch P, the urethane rubber has deformed to move against and exert pressure along the entire height of walls 22 and 24, to move into the relief recesses 28a and 2811 and into relief space 30, to move upwardly along the sides of the work piece W and above the normal lev-el of the pads top surface 12. Although not seen in FIGURE 4, the pad 10 al-so deforms endwise to exert pressure against `the end walls 42.

The usefulness and economy of t-he construction hereinabove described will now be understood. A tooling shop needs only to carry in stock extrusions 21 of a length sufficient to accommodate a demand for the longest possible press brake female die. A supply of extrusions would be maintained for different size die pads, su'ch ras die pads of 1" x l, 2" x 2, 3 x 2", etc. The end plates 42 are precut for fitting into the longiftudinal recesses of the respective extrusions. When an order comes for tooling for a particular job, the shop need only select the desired size of die pad and associated extrusion. Then the pad is cut to a requisite length and the extrusion is cut lto suficient length to receive the die pad and the end walls 42 therein, leaving a few inches of additional length at each end beyond each end wall 42. The only additional work is the machining neces- 4 sary -to effect connection of the end plates, and fthe order is completed.

It is understood `that the thickness of material in extrusion 21 outwardly of side walls 22 and 24 is designed to accommodate the greatest loadings to which the die pads 10 could be subjected within the range of their design ratings and considering that the die pads exert -uniform lateral pressure against the wall as if the pads were a solid liquid. By providing additional material to resist the increase in bending stress at the lower ends of walls 22 and 24 due to such loadings and to resist variation of the basic shape of the retainer chamber under loadings during use of a die pad, it will be seen that the use of extruded retainers 21 with die pads 10 solves the many problems noted hereinabove `as being associated with prior constructions of urethane rubber die retainers.

Some changes may be made in the construction and arrangement of the parts of our press br-ake die retainer without departing from the real spirit and purpose of our invention, and it is our intention to cover by our claims any modified forms of structure or use of mechanical equivalents which may reasonably be included within their scope.

We claim as our invention:

1. In a die Iretainer for a urethane rubber die pad where the die retainer provides an elongated die pad chamber having parallel side walls, end walls, support surfaces for the pad and a relief recess :centrally of the support surfaces, the improved die retainer characterized by the combination of an elongated body of extruded aluminum defining therein an elongated die-pad recess bounded by elongated upright parallel spaced side walls, elongated support surfaces for a die pad located in a horizontal plane perpendicular to the side walls and spa-ced below the upper edges of t-he side walls, -a relief space longitudinally of the body located centrally of the support surfaces, and end plates lon the extruded body projecting across the die-pad recess to define a die-pad chamber.

2. In a die retainer for a urethane rubber die pad where the die retainer provides an elongated die pad chamber having parallel side wal-ls, end walls, support surfaces for the pad and a relief recess centrally of the support surfaces, the improved die retainer characterized by the combination of an elongated body of extruded aluminum defining therein an elongated die-pad recess bounded by elongated upright parallel spaced side walls, elongated support surfaces for a die pad located in a horizontal plane perpendicular to the side walls Iand spaced below the upper edges of the side walls, a relief space Ilongitudinally of the body located centrally of the support surfaces, and the thickness of the material of the extruded body outwardly of the side walls increasing in thickness continuously in the direction downwardly from the upper edges of the side walls to the plane of the support surfaces, thereby providing increasing resistance to increasing bending stresses obtained with use of a urethane rubber die pad, and end plates on the extruded body projecting across the diepad recess to define a die-pad chamber.

3. In a die retainer for ya urethane rubber die pad where the die retainer provides an elongated die pad chamber having parallel side walls, end walls, support :surfaces for the pad and a relief recess centrally of the support surfaces, the improved die retainer characterized by the combination of an elongated body of extruded aluminum defining therein an elongated die-pad recess bounded by elongated upright parallel spaced side walls, elongated support surfaces for a die pad located in a horizontal plane perpendicular to the side walls and spaced below lthe upper edges of the side walls, a relief space longitudinally of the body located `centrally of the support surfaces, aperture means in said extrusion located in a plane perpendicular to the longitudinal axis of the extrusion and communicating with the die-pad recess of the extruded body, an end plate for projecting across the diepad recess to help define the die-pad chamber, and means on the end plate extending into said aperture means for securing the end plate to the extruded body so that forces applied against the end plate are transmi-tted to the extruded body.

4. An improved die pad retainer as set forth in claim 2 wherein there are aperture means in the extrusion extending through said side Walls and into the material outwardly of the side walls, the aperture means being located in a plane perpendicular to the longitudinal axis of the extrusion, Iand means on an end plate extending laterally of the end plate into said aperture means for securing the end plate to the extruded body.

5. An improved die pad retainer as set forth in claim 3 wherein the extrusion `delines longitudinal relief re- -cesses at the projected intersections of the side walls and the support surfaces.

References Cited by the Examiner UNITED STATES PATENTS 2,239,339 4/1941 Oeckl 72-60 2,781,849 2/1957 Bladergroen et a-l. 72-465 CHARLES W. LANHAM, Primary Examiner. R. D. GREFE, Assistant Examiner. 

1. IN A DIE RETAINER FOR A URETHANE RUBBER DIE PAD WHERE THE DIE RETAINER PROVIDES AN ELONGATED DIE PAD CHAMBER HAVING PARALLEL SIDE WALLS, END WALLS, SUPPORT SURFACES FOR THE PAD AND A RELIEF RECESS CENTRALLY OF THE SUPPORT SURFACES, THE IMPROVED DIE RETAINER CHARACTERIZED BY THE COMBINATION OF AN ELONGATED BODY OF EXTRUDED ALUMINUM DEFINING THEREIN AN ELONGATED DIE-PAD RECESS BOUNDED BY ELONGATED UPRIGHT PARALLEL SPACED SIDE WALLS, ELONGATED SUPPORT SURFACES FOR A DIE PAD LOCATED IN A HORIZONTAL PLANE PERPENDICULAR TO THE SIDE WALLS AND SPACED BELOW THE UPPER EDGES OF THE SIDE WALLS, A RELIEF SPACE LONGITUDINALLY OF THE BODY LOCATED CENTRALLY OF THE SUPPORT SURFACES, AND END PLATES ON THE EXTRUDED BODY PROJECTING ACROSS THE DIE-PAD RECESS TO DEFINE A DIE-PAD CHAMBER. 